Environmental Progress - Fall 2003

Phytoremediation Remedying Pollution From the Roots Up

New technology solar powered, aesthetically pleasing, and it works

Can a remedial technology be "green"? Is there an effective solar powered, aesthetically pleasing way to clean up numerous contaminants in soils and groundwater?

The project staff working at The LaSalle Electrical Utilities Superfund site believes there is. They are using phytoremediation - using green plants to remove pollution from soils and groundwater - to remove volatile organic compounds from the soils and groundwater.

Phytoremediation uses specific varieties of plants, known as hyperaccumulators, that absorb or "uptake" unusually large amounts of certain metals or other contaminants.

Poplar and willow trees are the plants of choice at the LaSalle site. These species were selected because they have been shown to be particularly effective at absorbing groundwater contaminated with the tetrachloroethylene and perchloroethlyene, as well as other volatile chemicals, found at this site. The trees take up contaminants through the roots, then they move into the tree itself and its leaves. Microbial action in the roots breaks down some of the contaminants before they reach the tree. The plants work by breaking down organic pollutants and acting as filters or traps that contain and stabilize metal contaminants.

On Superfund List

LaSalle Electrical Utilities was placed on the National Priorities List, or Superfund, in the early 1980s, primarily due to PCB contamination from the now bankrupt transformer manufacturer. The PCB contaminated soils were remediated through incineration, which was completed in 1993.

Cleanup of the solvents in the groundwater then began, and has continued since the early 1990s. The phytoremediation should be the last phase of the total remediation package.

The work at LaSalle is also serving as a demonstration plot. Dr. J. G. Isebrands, special consultant for the project, has planted several varieties of each species and will study not only their effectiveness at removing contamination, but their adaptability to the surroundings, including disease resistance.

There are 26 varieties of willows and 16 varieties of poplar. All varieties are known to be hardy in LaSalle County's climate, but are periodically analyzed for their value as a remedial technology.

Illinois EPA's project manager for LaSalle Electric Utilities, Rich Lange, reports that on a regular basis leaves, branches, and even entire trees are removed and sent to a laboratory to evaluate their effectiveness.

He and Isebrands then determine which varieties are doing the job most effectively.

Isebrands anticipates the results of these studies will aid decision makers across the country in determining the most appropriate remedial techniques to use at other sites.

The question of what to do with plants used for remediating hazardous waste sites depends on the type of plant and on the future land use. Plants like grasses are typically extracted and incinerated, since they contain the hazardous components they took from the soils. When this is done, the ash must be handled as a hazardous material. However, the volume of ash is only about one-tenth of what the contaminated soil would be. This can result in significant cost savings - in addition to not having to excavate and remove large quantities of soil.

Willow and poplar trees can continue growing since the contaminants are contained within the trees. If they were to be removed, they would have to be properly handled; if they remain in place, willows can live 25 to 30 years and poplars more than 50 years.

Phytoremediation is not new, but it is an emerging technology. It has been used across the country to clean up pollutants such as pesticides, solvents, explosives, oil, and landfill leachate. Grasses are being used to clean up petroleum in soils in Virginia; Indian mustard is being used to clean up heavy metals and radionuclides in New Jersey soils; and duckweed and parrotfeather are being used to clean up explosive wastes in the groundwater in Tennessee.

Considering that it is typically much less expensive and intrusive than standard technologies, phytoremediation can be a very appealing alternative to traditional remedial technologies.